The present invention relates to electro-optic imaging devices for three-dimensional (3D) display applications. More particularly, the present invention concerns a method and apparatus for volumetric 3D displays utilizing stacked, multi-layered, two-dimensional (2D), flat panel technology, such as non-conventional LCD technology.
With the continuously increasing demand for improved electronic imaging displays, and with the increasing bandwidth of computers, several 3D imaging display methods have been suggested, including stereovision, computer graphics, holography, vibrating or rotating screens, and split images, all of which have their advantages and drawbacks.
Stereovision has been increasingly developed in recent years; however, it is not a real 3D imaging method and therefore it has its limitations. Specifically, stereovision only takes into account binocular disparity (static parallax), but the other depth information, such as eye accommodation, convergence and motion parallax, are neglected. Another disadvantage is the need for viewing aids, such as eyeglasses and the like.
Computer graphics using 3D animation are also not real 3D. They give the impression of 3D information by shifting and/or rotating motion, and therefore, they have two basic drawbacks: first, a real, physiological 3D perception is not possible, and second, this method requires active intervention during perception, reducing attention and/or intervention for other actions.
Although conventional holography is a real depth 3D imaging method, it is not electronic, and it is therefore not a real-time display application. There are research and development programs on electronic holography at universities, but commercialization is so far not yet practical, due to the large space bandwidth requirements which at present necessitate the use of super computers.
Vibrating or rotating screen displays belong to another class of more recent, real depth imaging displays wherein a volume 3D image is created by lateral or rotational volume-sweeping of a 2D illuminated screen or disk. The disadvantage of this system obviously lies in the cumbersome opto-mechanical projection system.
Split image display refers to a relatively new method of 3D imaging, wherein an illusion of depth is created by projecting to the viewer""s eye, via Fresnel lenses, two pseudoscopic images of two different focal lengths, i.e., a foreground image and a background image. The two different focal contents force the viewer to constantly refocus his eyes, thereby creating an eye accommodation and convergence effect. Static and motion parallax also exist with this method. The method does not utilize any mechanical volume sweeping, however, its drawback obviously lies in the limited detailed depth information available from specific objects. For example, an object in the foreground will have a 2D appearance, even though the overall image creates a 3D illusion.
In two different attempts to achieve real depth, or volumetric, 3D displays without referring to mechanical volume sweeping, the use of multi-layered, stacked 2D sliced images or image contours is proposed.
The first proposal teaches the stacking of two types of 2D panels: namely, gas discharge, or plasma, panels on the one hand, and liquid vapor devices on the other. One disadvantage of plasma displays obviously is associated with the production and handling of devices based on vacuum tube technology. Another disadvantage lies in the limited resolutions achievable with this technology.
The second proposal, as described in U.S. Pat. No. 5,745,197, teaches the use of stacked, planar, light-absorbing elements consisting of conventional LCD panels sandwiched between polarizers and quarter-wave plates. For practical reasons, LCD devices may be divided into three classes: (a) devices including conventional pairs of polarizers, (b) devices including one single polarizer, and (c) polarizer-free devices. The reason for this division lies in the fact that polarizers absorb an important part, over 50%, of the display illumination. Therefore, conventional LCD devices, as taught by said patent, are disadvantageous because of the necessity to introduce additional elements such as polarizers, which significantly reduce the brightness, and as a consequence the number of stacked layers, or depth, in a device. The reduced brightness necessitates increased lamp power, which in turn increases power consumption and heat dissipation.
Another disadvantage of utilizing conventional LCD technology is the limited viewing angle. To reduce this problem, additional optical compensation layers, such as quarter wave plates, may be introduced. Such additional compensation layers, however, further complicate the system and increase its cost.
Also, by limiting the image display operation principle of the LCD to absorption modulation (absorptive grey shades), an essential part of image perception based on light scattering is lost. In addition, the necessity to apply a rear backlight is disadvantageous, from both the aspect of the varying quantity of light arriving from different layers, which again limits the achievable depth of the scene or object to be displayed, and from the aspect of additional geometrical depth requirements of the display.
Other examples of possible flat-panel media that may be used for stacking in multi-layered display assemblies are:
1) inorganic or organic, electroluminescent light-emitting diode (OLED) layers;
2) electrochromic layers; and
3) non-linear, electro-optic layers.
The disadvantages of each of these media are: under (1), their permanent color and light-absorbing characteristics, which limit the number and depth of the layers; under (2), their slow response times, which make them impractical for real-time applications; and under (3), their need for high-intensity illumination, which implies expensive and/or bulky light sources.
The general object of the present invention is to provide methods of, and devices for, real-depth, volumetric 3D electro-optical image displays wherein the 3D images are achieved by utilizing multi-layered structures of electro-optical flat panel display technology, and wherein each of these layers represents a slice through the object to be displayed.
It is a specific object of the present invention to provide a multi-layered structure by stacking an assembly of layers on top of each other, utilizing at least two plastic substrates folded as many times as necessary to achieve the desired number of layers.
It is a further object of the present invention to utilize suitable 2D flat panel media of very high transmittance, having low absorbance, low reflectance or low scattering, in the areas where no image is displayed, so that the 3D image composed of said media does not become obscured in depth, to obtain good quality 3D images having good optical clarity. Advantageously, suitable 2D flat panel media are chosen from non-conventional, polarizer-free liquid crystal (LC) media, including polymer-dispersed liquid crystals (PDLC) and derivatives thereof, such as nematic curvilinear aligned phases (NCAP) and polymer stabilized cholesteric textures (PSCT) or guest-host (GH) dichroic or pleochroic LCs, and combinations and derivatives of these non-conventional media. Such media allow maximal light utilization because they minimize losses of polarizer and in-depth absorption, so as to allow larger depths and numbers of layers to be realized in 3D display devices.
Still another object of the present invention is to provide suitable illumination systems so as to make the image visible during operation of the 3D devices. Specifically, side-coupled illumination, in combination with scattering PDLC layers, enables homogeneous illumination of the object through its 3D depth, so as to allow larger depths and numbers of layers to be realized in 3D display devices.
A yet further object of the present invention addresses the attachment of suitable optical elements on top of a multi-layered imaging (MLI) stacked assembly for the purpose of 3D image and 3D depth enlargements (3D object scaling).
The present invention also provides electronic methods and systems for simultaneously driving and addressing the pixels of the 3D tensor (voxels).
In accordance with the present invention, there is therefore provided a multi-layered imaging device for three-dimensional image display, comprising a plurality of two-dimensional layers superposed in the third dimension, each of said layers having two major surfaces and at least one peripheral edge, said layers being made of a material selected from the group of non-conventional, polarizer-free liquid crystal materials including polymer-dispersed liquid crystals (PDLC) and derivatives and combinations thereof, wherein the exposure of at least one of said layers to illumination allows the transmission of light with minimal losses, facilitating utilization of a maximal number of layers for imaging a three-dimensional display.
Some of the intrinsic properties of the proposed 3D MLI devices of the present invention are unique, and include, among others, real-volume 3D image display, with theoretically possible maximal fields of view of 360xc2x0, both vertically and horizontally, and real-time, updateable and time-sequenced 3D image displays. These properties enable a large number of possible applications, each of which may exploit existing imaging capture systems. A non-exhaustive list of such imaging capture systems may include a set of cameras and sensors positioned in space, from which the spatial 3D information may be processed and distributed to the display layers; one or more cameras equipped with a laser or other range finder, so that the image data may be split by image depth and transferred to the individual display layers; and a set of radiation sources, precisely positioned in space, emitting collimated and confined beams which scan the object from which the transmitted, reflected or scattered data are collected by 2D sensor arrays and transferred to the individual image layers.
3D imaging of active (x-ray, MRI, etc.) and passive (radioactive emission) computer tomography seems to be a natural application of the present invention, because of the nature of the image acquisition, which is of a multi-layered nature. For example, in CT or MR imaging of the skull, the number of sliced images is a maximum of about 150 or 50, respectively, which are often reduced for economic reasons. Object reconstruction is computer time-intensive, involving very expensive workstations and programs. The present invention has great potential in reducing the time and cost of object reconstruction, because the sliced layer information may be directly fed into the 3D MLI.
Furthermore, as discussed above, the present invention enables real volume depth 3D image display, which is not possible with conventional display technology. Therefore, 3D MLI dramatically reduces the quantity of computer interaction, such as object rotation, etc., which is necessary with conventional displays in order to view the object from different angles and to produce 3D object information.
Additionally, 3D MLI techology enables actual four-dimensional (4D) display. In other words, a 3D object may be displayed as a time-dependent, 4D object. This is of great importance, as it allows temporal evolution of physiological changes in a patient to be monitored and imaged in 3D.
For any engineer, it is of importance in the designing phase to be able to demonstrate the designed object in a virtually real model. Therefore, 3D MLI is a most suitable application for modelling and prototyping of the present invention, because it is a real-depth 3D image display approach.
3D solid or computer graphic methods exist, each of which has its limitations. For example, the solid, layered photopolymer methods create a real solid model of the designed object. It takes several hours or days, however, until this solid model is available, and another identical time lapse if the model needs to be updated.
Furthermore, the present invention enables real-volume 3D image display, which is not possible with conventional computer graphics technology. Therefore, 3D MLI dramatically reduces the quantity of computer interaction, such as object rotation, etc., which is otherwise necessary in order to view the object from different angles so as to produce 3D object information.
As the 3D MLI technology is updateable in real-time, quite obviously it calls for 3D video and television applications. 3D television is of importance especially in such applications where 3D is an asset for producing enhanced depth perception or reality. A first example of such applications is aircraft navigation, where real-depth 3D images would assist the pilot during maneuvering or landing operations. A second example is 3D endoscopic displays in medicine, which, with the present invention, would become easier and more comfortable to use as no headgear devices are needed and consequently, may be simultaneously viewable to a large number of observers. A third example would be computer virtual reality and similar 3D television applications, which again would be easier and more comfortable, and viewable to an increased number of simultaneous viewers.